Means for shrinking flanged vitreous syringe barrels



y 1964 s. N. BLACKMAN MEANS FOR SHRINKING FLANGED VITREOUS SYRINGE BARRELS Original Filed Oct. 2, 195a United States Patent Seymour N.

assignments, Rutherford,

This invention relates to a new and improved method and means for shrinking flanged vitreous syringe barrels.

This application is a continuation of my prior application for United States Letters Patent, Serial No. 613,541, filed October 2, 1956, and entitled Method and Means for Shrinking Flanged Vitreous Syringe Barrels.

In the manufacture of hypodermic syringes, it is well known to employ so-called interchangeable syringes, i.e., syringes in which any one of a group of plungers can be used with any one of a group of barrels, thus avoiding the difficulties formerly attendant upon individually matching plungers with syringe barrels to obtain the re quisite close fit.

With interchangeable syringes, all syringe barrels of a particular size will fit perfectly with plungers made for that size. However, the hollow mandrels on which the tubing conventionally has been shrunk tended to warp when heated to the high shrinking temperature. Moreover, said mandrels have been difficult and expensive to manufacture to the necessary very close tolerances because their interior hollow bodies affected their dimensional stability during processing. Accordingly, such mandrels have proven hard to maintain, short-lived and expensive.

It is an object of the present invention to provide a method and means of the character described wherein the foregoing difliculties are avoided.

It is another object of the present invention to provide a method overcoming the enumerated difliculties which can be practiced easily and at a low cost.

It is another object of the present invention to provide a mandrel for use in practicing the method of the present invention which mandrel has none of the drawbacks alluded to above.

It is another object of the present invention to provide a mandrel of the character described which is simple and inexpensive to make and use.

Other objects of the invention in part will be obvious and in part will be pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts which will be exemplified in the device and method hereinafter described and of which the scope of application will be indicated in the appended claim.

FIG. 1 is a side view of a mandrel constructed in accordance with the present invention, the same being shown with a flanged syringe barrel disposed above it and with its lower end located in a mounting;

FIG. 2 is an enlarged fragmentary longitudinal sectional view of the mandrel shown in FIG. 1 with a syringe barrel disposed thereon at an early stage in the shrinking process;

FIG. 3 is a view similar to FIG. 2, but illustrating a syringe barrel at an intermediate stage of the shrinking process;

FIG. 4 is a view similar to FIG. 2 taken after shrinking of the syringe barrel has been completed; and

FIG. 5 is an enlarged transverse sectional view taken substantially along the line 55 of FIG. 1.

Referring now in detail to the drawings, the reference numeral denotes a mandrel embodying the instant invention. Said mandrel constitutes an elongated body and 3,141,754 Patented July 21, 1964 is fabricated as a single piece from stainless steel or other suitable heat-resistant material. Pursuant to the invention, said mandrel principally constitutes a solid, i.e., not hollow, cylindrical upper forming surface 12 the lower end of which is in one piece with a squat pendent threaded shank 14 of reduced section that is secured into a central tapped bore 16 in the top wall 18 of a hollow socket 29 having a larger external diameter than that of the forming surface. The radially protruding portion of the top wall 18 of said socket forms a shoulder 22 perpendicular to the longitudinal axis of the mandrel to thus provide a supporting flange. The socket also includes a downwardly tapered lower end 24 the inside of which is hollow to form a passageway that communicates with the hollow interior of the socket.

The shoulder 22 includes two annular and concentrically disposed sets 26, 28 of critically located upper termini (see FIG. 5) of bores that run to the interior of the socket. One set 26 is located adjacent the base of the forming surface so as always to be in communication with any air space one boundary of which is the lower end of the forming surface 12.

The termini 26 will not be covered by the flange 30 .of a syringe barrel 32 to be shrunk due to the overly large diameter thereof and the consequent spacing of the inner wall 34 of the syringe barrel from the forming surface. The other set 28 of termini is spaced radially from the forming surface a distance such that the flange 30 of the syringe barrel will cover the same when such barrel is slipped over the forming surface. The termini of each set preferably are equiangularly spaced apart, and a termini of each set is located midway between adjacent termini of the other set to ensure uniformity in shrinking as will become apparent hereinafter.

The socket is attached in any conventional manner as by a conduit 36 to a vacuum pump or the like.

The method of the present invention is as follows: First an open-bottomed flanged syringe barrel preform 32 to be shrunk is ensleeved over the forming surface 12 of the solid mandrel 10 until the flange 30 is seated on the shoulder 22. It will be noted that the mandrel protrudes from the open bottom of the barrel. At this time the set of termini 26 will open into the annular space between the forming surface and the inner wall 34 of the syringe barrel. The termini of the set 28 are overlain by the under surface of the flange but are not blocked thereby.

The entire syringe barrel then is heated to a suitable pre-softening temperature appropriate for the material of the syringe barrel, e.g., 1100 F. for borosilicate glass. This is accomplished by playing a flame substantially uniformly over the entire syringe barrel from the top thereof to the bottom and including the flange for a time suflicient to heat the barrel to pre-softening temperature.

The next step in the method is to increase the temperature of the bottom and the flange 30 of the syringe barrel until they become mobile, e.g., 1300 F. At the same time the air pressure in the socket is reduced below atmospheric pressure as by opening a valve to connect the same to a vacuum pump. The temperature of the outer end and flange of the syringe barrel is raised in any conventional manner by playing flames 38 and 40 thereon. As a result of such heating and the pressure of the ambient atmosphere, the glass at the top collapses against and conforms to the mandrel. At the same time, as a result of said heating and the forces of gravity and the ambient atmosphere, the flange 30, in line with the annular series of openings 28, will seat against the shoulder 22 to obstruct air flow through these openings. Thus the annular space between the barrel and the mandrel is isolated from the atmosphere.

It is within the scope of the invention to conform the bottom of the barrel to the mandrel during the presoftening step if the pressure in the socket is lowered at such time; the pre-softening flame being sucked into the syringe barrel by the reduced pressure so as to play on both inner and outer surfaces of the bottom of the barrel and thereby raise it to mobility. The flange may be conformed to the shoulder surface at the same time or in the same manner.

FIG. 2 shows the barrel and mandrel immediately after pre-softening and while the flames 38, 40 are heating the bottom and top of the barrel to mobility, while in FIG. 3 the barrel and mandrel are shown with the upper end of the barrel conformed to the forming surface of the mandrel and the flange engaging the shoulder 22 to obstruct openings 28.

It is desired to point out that while in the pre-softening step the syringe barrel and mandrel are uniformly heated, only the upper end and the flange of the syringe are locally heated during the sealing steps.

When the top and bottom seals referred to above have been accomplished, the selective heating of the bottom and flange of the syringe barrel is stopped and a general uniform shrinking of the barrel is effected by movement of a flame 42 from the end of the inverted syringe barrel to the flange thereof. The shrinkage is caused by atmospheric pressure; a vacuum now being present between the inner wall 34 of the syringe barrel and the forming surface 12 of the mandrel, and the barrel wall being progressively heated by the flange 42 to a temperature at which it is rendered plastic. The vacuum can be created and easily maintained after the top and bottom seals are made because the termini 26 are not blocked off until shrinkage of the syringe barrel is complete as shown in FIG. 4.

The above described mandrel and method can be used and practiced respectively with any suitable apparatus. Such apparatus could be adapted to hold several sockets and would have means to provide the required heating and to create the required vacuum at appropriate times.

A typical machine usable for this purpose is that disclosed 1 in Patent No. 2,684,556, dated July 27, 1954, to Molinari.

Mandrels of different sizes can, of course, be made and used in accordance with the instant invention, so that interchangeable syringe barrels of different sizes can be fabricated.

Although the invention has been described with respect to use in connection With a syringe barrel which has a full-open outer end at the time of shrinking, it may be practiced with equal facility on syringe barrels that are Wholly or partly closed during shrinking.

It thus will be seen that there are provided a method and means which achieve the several objects of the invention and are well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention, and as various changes might be made in the embodiment above set forth, it is to be understood that all matter herein described, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

I claim:

Apparatus for vacuum shrinking the outer bore at an end of a preformed glass open-ended tube in the manufacture of a glass hypodermic syringe barrel from said tube comprising a solid cylindrical elongated mandrel assembly provided with smooth continuous outer side surfaces dimensioned for presenting, after shrinking of the preformed, open-ended tube, a close fit to the inside cylindrical wall of the tube into which said mandrel has been inserted, said mandrel having a shoulder portion extending outwardly at the lower end thereof in a direction perpendicular to the axis of the mandrel, said shoulder supporting the lower end of said preform after said lower end is sealed, said shoulder being provided with a plurality of uniformly distributed circumferentially placed passageways, each of said openings being in longitudinal alignment with the body of said mandrel and being in air communication with the interior space of the tubular preform, being thereby adapted for evacuation of the space between the unshrunk tubular preform and the lower portion of the lower end of said preform, vacuum pump means connected to said openings, sealing means to seal the top of said tubular preform, heating means located exteriorly of the preform mounted on said mandrel for imparting heat in a direction away from said shoulder and directly to the upper end of said preform, this heat being suflicient to uniformly soften the outer circumference of the glass of the preform above the shoulder of said mandrel for a predetermined longitudinal area corresponding to the height dimension of the shrunken barrel whereby after sealing both ends of said preform the pres- .sure differential caused by the application of vacuum through said openings causes the mandrel-conformed shrinkage at the lower wall areas of the preform located above the shoulder of said mandrel.

References Cited in the file of this patent UNITED STATES PATENTS 

